A high-volume foam spray gun assembly having a mixing section comprising a chamber bore, and a mixing chamber movingly disposed within the chamber bore. The mixing chamber further includes a first lateral orifice, a second lateral orifice, a central mixing bore, and a central mixing bore outlet. The spray gun assembly is operable to spray a foam product out of the spray tip at a rate of in the range of about 10 lbs/min to about 100 lbs/min. The first lateral orifice has a first lateral orifice diameter in the range of at least greater than 0.1 inches. The second lateral orifice has a second lateral orifice diameter in the range of at least greater than 0.1 inches.